Unless it’s patentable, there’s no economic incentive for any one farmer or farm conglomerate to invest in this research. It would require government or non-profit research. And in a world of scarce resources, funding research on a luxury food item would strike many as a waste of taxes or philanthropic funds.
(I’m not saying it’s wasteful, learning the secrets of truffle reproduction could unlock a new branch of scientific study. Just explaining why this is.)